Snowpack trends across Canada's largest river basin using three decades of manual snow surveys and ERA5-Land data

Abstract. In the Mackenzie River basin (MRB), end-of-season snowpack volume is an essential indicator for spring flood potential, wildfire risk, and hydroelectric power generation, and it underpins cold region hydrological research and monitoring. This study presents a trend analysis of 31 years of previously unpublished manual snow survey data from Canada's Northwest Territories (NWT) and incorporates snow survey data from other jurisdictions within the MRB to determine how the end-of-season snow water equivalent (SWE) has changed. We then use this independent SWE dataset to evaluate SWE trends from ERA5-Land reanalysis data for its suitability as an additional data source for assessing interannual variability in SWE. Spearman rank correlation analysis demonstrated moderately strong agreement in SWE trend variability between datasets, with a stronger agreement for sites in the NWT. We found that climate variables were the dominant drivers of residuals. Over the 31-year period, SWE trends exhibited substantial spatial variability within and between sub-basins and ecozones. No consistent latitudinal or elevational trends emerged, highlighting the complex, landscape-dependent influence of warming air temperatures on snowpack accumulation. These findings are relevant to decision makers who need an improved understanding on how SWE trends are changing at a basin scale. These results demonstrate that the combined use of manual snow surveys and gridded reanalysis datasets can be used to strengthen long-term snow monitoring and research in the Northwest Territories.